DESCRIPTION (applicant's description): Ribonuclease P (RNase P) is a ribonucleoprotein complex that catalyzes the essential 5' maturation of precursor tRNA (pre-tRNA). Both the protein and RNA subunits are essential for iii vivo activity; however, the bacterial RNA component catalyzes pre-tRNA cleavage iii vitro in high salt. Mechanistic and structural investigations of this enzyme are crucial as RNase P and the ribosome are the only ribozymes that function as true enzymes in vivo. In the previous grant period, we solved the first structure of the protein component of ribonuclease P and demonstrated that the protein enhances catalytic efficiency by binding the leader sequence of the precursor-tRNA substrate. This function places the protein component near the active site and for the first time demonstrates that the RNA and protein components both contribute to molecular recognition properties. We propose to continue investigating the structure-function properties of the Bacillus subtilis RNase P protein using a combination of biochemical (mutagenesis, crosslinking, kinetic analysis, isotope effects, modification interference, and spectroscopy) and x-ray crystallographic structural techniques. Specifically, we aim to: (1) explore the molecular recognition properties of the single-strand RNA binding cleft in the RNase P protein and to determine the position of this site relative to the P RNA; (2) delineate the P protein/P RNA binding surface and define the role of specific contacts in catalysis; (3) determine the position of catalytic metal sites and dissect the catalytic mechanism; and (4) extend the resolution of the RNase P protein structure, determine the structures of P protein-oligonucleotide complexes and site-specific variants of P protein, and solve the structure of native RNase P holoenzyme and holoenzyme-substrate complexes. Our long-term goal is to further our understanding of (1) the mechanisms of catalysis used by ribozymes as compared to protein enzymes, and (2) the structures and energetics of RNA binding proteins and protein/RNA complexes. RNase P is an ideal enzyme to compare catalytic strategies in protein and RNA enzymes since it functions in a biosynthetic pathway in vivo. Furthermore, the unique collaboration between the protein and RNA subunits may provide insight into the evolution from RNA to protein catalysts. Finally, RNase P has potential medical applications as both a novel antibiotic target, since it is an essential prokaryotic enzyme, and as a novel tool to specifically cleave mRNA species in vivo in gene therapy applications.